I need to time the operation of a command-line utility (specifically nslookup)
from within a python program I'm writing. I don't want to use python's timeit
function because I'd like to avoid python's subprocess creation overhead. That
leads me to the standard UNIX time function. So for example, in my bash shell,
if I enter:
$ time nslookup www.es.net 8.8.4.4
I get:
Server: 8.8.4.4
Address: 8.8.4.4#53
Non-authoritative answer:
www.es.net canonical name = www3.es.net.
Name: www3.es.net
Address: 128.55.22.201
real 0m0.069s
user 0m0.006s
sys 0m0.004s
The first lines are the result of an nslookup of the IP address of "www.es.net"
using the server at 8.8.4.4 (Google's public DNS server b).
The last three lines are what I'm after: the real elapsed wall-clock time, the
time spent in user space and the time spent in kernel space.
However, if I try the same operation in the python interpreter using
subprocess.Popen like so:
>>> import subprocess
>>> result = subprocess.Popen(['time', 'nslookup', 'www.es.net', '8.8.4.4'],
>>> shell = False, stdout = subprocess.PIPE, stderr =
>>> subprocess.PIPE).communicate()
>>> print result
('Server:\t\t8.8.4.4\nAddress:\t8.8.4.4#53\n\nNon-authoritative
answer:\nwww.es.net\tcanonical name =
www3.es.net.\nName:\twww3.es.net\nAddress: 128.55.22.201\n\n', ' 0.06
real 0.00 user 0.00 sys\n')
And the timing information I'm after has been truncated to two digits after the
decimal. It appears that Popen is applying a default format. If I do explicit
formatting:
>>> time = result[1].lstrip().split(' ')[0]
>>> formatted_time = '{: >7.3f}'.format(float(time))
>>> print formatted_time
0.060
I get three digits, BUT that third digit isn't real, the format operation has
simply appended a zero. So:
1) how can I recover that third digit from the subprocess?
2) is there a more pythonic way to do what I'm trying to do?
python 2.7, OS-X 10.8.2
Thanks in advance -
Bill Wing
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